Tag Archives: VVol

Moving from an RDM to a VVol

Migrating VMDKs or virtual mode RDMs to VVols is easy: Storage vMotion. No downtime, no pre-creating of volumes. Simple and fast. But physical mode RDMs are a bit different.

As we all begrudgingly admit there are still more than a few Raw Device Mappings out there in VMware environments. Two primary use cases:

  • Microsoft Clustering. Virtual disks can only be used for Failover Clustering if all of the VMs are on the same ESXi hosts which feels a bit like defeating the purpose. So most opt for RDMs so they can split the VMs up.
  • Physical to virtual. Sharing copies of data between physical and virtual or some other hypervisor is the most common reason I see these days. Mostly around database dev/test scenarios. The concept of a VMDK can keep your data from being easily shared, so RDMs provide a workaround.

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Do thin VVols perform better than thin VMDKs?

Yes. Any questions?

Ahem, I suppose I will prove it out. The real answer is, well maybe. Depends on the array.

So debates have raged on for quite some time around performance of virtual disk types and while the difference has diminished drastically over the years, eagerzeroedthick has always out-performed thin. And therefore many users opted to not use thin virtual disks because of it.

So first off, why the difference?

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Comparing VVols to VMDKs and RDMs

I have been talking a lot about Virtual Volumes (VVols) lately with customers and when I describe what they are a frequent response is “oh so basically RDMs then?”. ..

…ugh sorry I just threw up in my mouth a bit…

The answer to that is an unequivocal “no” of course, but the question deserves a thorough response.

So first let’s look at how they are the same, then let’s look at their differences. And not just how they compare to RDMs, but also VMDKs as you traditionally know them.

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Importing a VVol Snapshot with PowerCLI

This is all very exciting for me, finally able to really start blogging about VVols in earnest. As you may or may not be aware we (Pure Storage) currently have our VVol implementation in beta. So I can finally start digging into some VVol work. Not going to get into implementation details just yet, but instead a quick walkthrough of importing a VVol snapshot with PowerCLI.

First, enjoy a poorly photoshopped Back To the Future reference:

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